The basic components of a conventional plasma arc torch includes a body, an electrode mounted in the body, a nozzle defining an orifice for a plasma arc, a source of ionizable gas, and an electrical supply for producing an arc in the gas. Upon start-up, an electrical current is supplied to the electrode (generally a cathode) and a pilot arc is initiated in the ionizable gas typically between the electrode and the nozzle, the nozzle defining an anode. A conductive flow of the ionized gas is generated from the electrode to the work piece, wherein the work piece then defines the anode, and a plasma arc is thus generated from the electrode to the work piece.
The pressure and flow of gas to the torch must be precisely controlled during start-up, operation, and shut down. Such control has previously been undertaken by a variety of methods including e.g., using a fixed orifice with a by-pass valve or a motor controlled pressure regulator. However, these conventional approaches can be problematic. For example, a fixed orifice provides only a fixed flow rate for a specific inlet pressure while motor controlled regulators add significant complexity and cost to a plasma arc torch system.
Accordingly, a control system for a plasma arc torch that can modulate both gas pressure and flow would be useful. A flow control system for a plasma arc torch that modulates both gas pressure and flow without adding undue complexity and cost to a plasma arc torch system would also be useful. These and other advantages of the present invention will be apparent from the description that follows.